Fuel flow control apparatus for gas turbine engines



May 20, 1969 E. H. WARNEJ ETAL 3,444,633

. FUEL FLOW CONTROL APPARATUS FOR GAS TURBINE ENGINES Filed Nov. 14,1966 United States Patent 3,444,688 FUEL FLOW CONTROL APPARATUS FOR GASTURBINE ENGINES Eugene Harold Warne, Shirley, Solihull, and GeoffreyAlbert Long, Sutton Coldfield, England, assignors to Joseph Lucas(Industries) Limited, Birmingham, England Filed Nov. 14, 1966, Ser. No.594,210 Int. Cl. F01c 9/02; F02d 9/08; F01d 17/00 U.S. Cl. 6039.28 3Claims ABSTRACT OF THE DISCLOSURE Apparatus for controlling the supplyof fuel to a gas turbine engine comprises a throttle slidably mounted ina body to control flow of fuel through a passage in the body, a pistonconnected to the throttle and disposed in a cylinder in the body, arestricted passage between the upstream side of the throttle and one endof the cylinder, a plunger coaxially and slidably mounted within thepiston, a manually operable control for the plunger, passage means inthe plunger through which fuel can flow to drain, at a rate which isdependent upon the relative positions of the plunger and piston, andmeans providing a force on the piston to oppose the fuel pressure atsaid one end of the cylinder to enable equilibrium conditions to beobtained.

This invention relates to fuel flow control apparatus for gas trubineengines and is primarily applicable to engines in which the quantity offuel required for acceleration in addition to that required for normalsteady running of the engine at any speed is not highly critical.

The object of the invention is to provide apparatus for controlling thesupply of fuel to a gas turbine engine, in a simple and convenient form.

In accordance with the present invention, apparatus for controlling thesupply of fued to a gas turbine engine comprises a body, a throttleslidably mounted in the body and arranged to control the supply of fuelalong a passage in the body, the body defining a cylinder containing apiston connected to the throttle for coaxial movement therewith, passagemeans in the body arranged to supply fuel at the pressure obtaining atthe upstream side of the throttle to the cylinder at one end of thepiston, a plunger which is coaxial with the piston and relativelyslidable therein, a manually operable control for the plunger, furtherpassage means in the plunger, in accordance with the relative positionof the plunger and the piston to control the drain of fuel from said oneend of the cylinder, and means providing a force on the piston tendingto oppose that provided by pressure of the fuel in said one end of thecylinder, thus enabling equilibrium conditions of the piston to beobtained.

The invention will now be described by way of example with reference tothe accompanying drawing which illustrates diagrammatically a fuelsupply system for a gas turbine engine.

The system comprises a main pump 10 of the swashplate type and arrangedto be driven through a shaft 11 from the engine with which the system isassociated. Associated with the main pump 10 and enclosed within thesame housing is a piston and cylinder type servo mechanism 12, and agovernor device 13 arranged to modify the servo mechanism 12. To thepump 10 is an inlet passage 14 from a reservoir (not shown) there being,between the reservoir and the pump 10, a centrifugal boost pump 15 and afilter 16. The main pump 10 delivers fuel into a passage 17 leading toburners in an engine indicated diagrammatically at 18. The servomechaice nism 12 is controlled primarily by the pressure differencebetween the inlet and the outlet of the pump 10 in known manner.

Also controlling the servo mechanism 12 is the governor 13 and a device19 which is responsive, through passages 20, 21, to the pressuresobtaining at the upstream and downstream sides of the engine compressor.This device contains a valve 22 which is arranged to control thepressure in a passage 23 leading to the servo mechanism 12. There isalso a device 24 sensitive to temperature conditions in the engine andarranged also to modify the position of the valve 22 in the device 19.

Between the pump 10 and the burners in the engine 18, in the passage 17,there is provided apparatus, which forms the subject of this invention,for controlling the flow of fuel to the engine and there is also a shutoff cock 25 for cutting off the supply altogether to stop the engine,with the cock 25 being manually operable by a lever 26.

This apparatus is enclosed within a body indicated by numeral 27 throughwhich is formed a bore containing a slidable throttle rod 28 one end ofwhich has tapering grooves 29 to enable fuel to How through anenlargement of the bore in the body 27, past an annular metering edge 30disposed between inlet and outlet portions of the passage 17 indicatedby 17a and 17b respectively. The outlet 17b communicates with theburners 18 in the englue.

The opposite end of the throttle rod 28 is formed integrally with apiston 31 slidable in a cylinder 32 formed as an enlarged extension ofthe bore in the body 27. Communicating with the end of the cylinder 32nearer to the throttle rod 28 is a passage 33 containing a restrictor inthe form of a pair of orifices 34, 35 in series, with this passage beingsubjected to the pressure of fuel at the upstream side of the meteringedge 30, through a passage 36 affording a flow path from the upstream tothe downstream sides of the metering edge 30. The passage 36 has tworestrictors 37, 38 in series so that the main flow to the burners takesplace through the portion of the passage 17 designated 17b.

This arrangement in the passage affords a liquid potentiometer, and anintermediate pressure from which is applied through a further passage 39to the opposite end of the piston 31 in the cylinder 32. The portion 17bof the passage 17 also contains a valve 40 which is provided to ensurethat flow only takes place to the burners in the engine 18 underpressure.

Slidably mounted within the piston 31 and throttle rod 28 is a coaxialplunger 41 in a closed ended bore 42 extending from the end at which thepiston 31 is disposed, with the wall of the throttle rod 28 beingpierced by a hole 43 normally opening into the end of the cylinder 32 atthe side of the piston 31 at which the throttle rod 28 is provided. Theplunger 41 has an annular groove 44 and a central passage 45, with thelatter communicating with the closed end of the bore 42 which, in turn,has a radial passage 46 leading, through a passage 47, to the inletpassage 14 of the pump 10 or other low pressure part of the system.

Connected to the plunger 41 to enable its position to be controlled byan operator, is a rod 48. Between the plunger 41 and the piston 31 is acompression string 49 which, in the event of a failure in the normalcontrol apparatus in the fuel system, causes movement of the plunger 41to move the throttle to its fully open position.

In this event, emergency fuel supply to the engine would be controlledby the shut off cock 26 in the system.

In use, steady running conditions are maintained by positioning thepiston 31 by a balance of the pressures 3 at its opposite sides. This isachieved by allowing a drain through the orifice 43, the annular groove44, the passage 45 to the bore 42 and thence out through the passage 46to the passage 47.

If it is desired to accelerate the engine to a new steady running speedit is not only necessary to open the throttle but it is also necessaryto provide additional fuel for acceleration purposes. To achieve this,the rod 48 is first moved manually to a position which, when equilibriumconditions are again established, will correspond to the requiredthrottle opening for the new steady running conditions. Movement of therod 48 causes the plunger 41 to move (to the right in the drawing) tocut off communication between the orifice 43 and the annular groove 44.Pressure therefore builds up in this end of the cylinder 32 to move thepiston 31 until such communication is again possible whereuponequilibrium will become reestablished. The rate of movement of thepiston 31 will be dependent upon the size of the orifices 34, 35 in thepassage 33. Such movement of the piston 31 will result in an additionalquantity of fuel, which would normally be drained through the orifice43, being delivered to the engine through the throttle. In the oppositeend of the cylinder 32 there is also a less significant displacement offuel through the passage 39 and into the passage to the burners 18through the orifice 38, which is larger than the orifice 37, with theadditional quantity supplied by these means being the required amountfor acceleration, and this additional fuel supply ceases when the piston31 stops upon commencement of the drain through the orifice 43 toreestablish equilibrium conditions.

If it is desired to decelerate the engine, the rod 48 is moved in theopposite direction by the desired amount. This results in movement ofthe plunger 41 in the same direction, (to the left in the drawing). Theorifice 43 now communicates fully with the annular groove 44 thussubstantially increasing the drain from the cylinder 32 and reducing thefuel quantity delivered to the engine by creating a greater demand atthe cylinder 32, to be drained through the orifice 43. The pressure atthis end of the cylinder 32 will fall to permit the piston to move underthe influence of pressure acting from the passage 39. This will thusreduce the throttle opening until equilibrium conditions are againestablished.

The characteristics of the acceleration and deceleration is governed bythe additional flow in the case of acceleration and the reverse in thecase of deceleration. These flows are, in turn governed by the size ofthe orifices 34, 35 in acceleration conditions, and by the sizes of theorifices 37, 38 in the deceleration conditions.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent is:

1. Apparatus for controlling the supply of fuel to a gas turbine engine,comprising a body, a throttle slidably mounted in the body forcontrolling the supply of fuel along a passage in the body, the bodydefining a cylinder, a piston in the cylinder connected to the throttlefor coaxial movement therewith, passage means in the body arranged tosupply fuel from the upstream side of the throttle to the cylinder atone end of the piston, said passage means having restrictors therein, aplunger coaxial with the piston and relatively slidable therein, amanually operable control for the plunger, further passage means in theplunger arranged, in accordance with the relative postions of theplunger and the piston, to control the drain of fuel from said one endof the cylinder, and means providing a force on the piston tending tooppose that provided by the pressure of the fuel in said one end of thecylinder, thus enabling equilibrium conditions of the piston to beobtained.

2. The apparatus as claimed in claim 1 including spring means locatedbetween the plunger and piston to cause movement of the plunger to movethe throttle to its fully open position in the event of a failure in thenormal control apparatus by the establishment of equilibrium conditionstherein.

3. A fuel supply system for a gas turbine engine having burnerscomprising a pump arranged to obtain a supply of fuel from a reservoir,means defining a fuel passage between the pump and the burners in theengine, and apparatus for controlling the supply of fuel along saidpassage, said apparatus comprising a body, a throttle slidable mountedin the body for controlling the supply of fuel along a passage in thebody, the body defining a cylinder, a piston in the cylinder connectedto the throttle for coaxial movement therewith, passage means in thebody arranged to supply fuel from the upstream side of the throttle tothe cylinder at one end of the piston, said passage means havingrestrictors therein, a plunger coaxial with the piston and relativelyslidable therein, a manually operable control for the plunger, furtherpassage means in the plunger arranged, in accordance with the relativepositions of the plunger and the piston, to control the drain of fuelfrom said one end of the cylinder and means providing a force on thepiston tending to oppose that provided by the pressure of the fuel insaid one end of the cylinder, thus enabling equilibrium conditions ofthe piston to be obtained.

References Cited UNITED STATES PATENTS 908,224- 12/1908 Eckland 251-38XR 3,139,892 7/1964 McRoberts 39.28 XR JULIUS E. WEST, Primary Examiner.

US. Cl. X.R. 13718;25l---38

